ION PAIRING REAGENTS AND BUFFERS

Transcription

1 ON PRNG REGENTS ND UFFERS

2 ULTRPURE ON PRNG REGENTS ND UFFERS The dvantages of on Pair hromatography on Pair hromatography is a method for improving the separation of charged analytes. n the resolution of organic ions with conventional HPL methods, use of ion pair reagents can enhance peak shape and retention time when common remedies such as modifying eluent ratios or changing n the past, chromatographic separation of charged analytes has been achieved by ion suppression (the careful adjustment of the mobile phase ph to result in a nonionized analyte). Determining the optimum mobile phase ph in ion suppression, however, often requires extensive method development. Samples containing more than one ionizable component were often unusable. The limitations of ion suppression led to the development of a new, more generally applicable approach to separation of ionized components: ion pair chromatography. Developed by Dr. Gordon Schill in 1973, ion pair chromatography relies upon the addition of ionic compounds to the mobile phase to promote the formation of ion pairs with charged analytes. These reagents are comprised of an alkyl chain with an ionizable terminus (figure 1). When used with common hydrophobic HPL phases in the reversed-phase mode, ion pair reagents can be used to selectively increase the retention of charged analytes (figure 2). stationary phase fail. on Pair Reagent + _ D N ON nalyte Figure 1. Quaternary mine (Q-Series) on Pair Reagent. on Pair Reagent + _ D N ON Silica Support -18 hain Length nalyte Figure 2. Quaternary mine (Q-Series) on Pair Reagent interacting with -18 Support. 48

3 ULTRPURE ON PRNG REGENTS ND UFFERS lthough ion exchange chromatography has become a popular mode of separation, it is not useful in all situations. The advantages of ion pair chromatography over ion exchange chromatography are: Simple preparation of buffers Wide choice of carbon chain lengths for improved retention and separation Significantly reduced separation time Simultaneous separation of both ionized and nonionized solutes Highly reproducible results mproved peak shape Regis Provides a hoice of Reagents Regis manufactures both ultrapure anionic Sulfonate (S-Series) and cationic Quaternary mine (Q-Series) ion pair concentrates in the following alkyl chain lengths: pentyl, hexyl, heptyl, octyl, and dodecyl. lkyl chains are represented by cardinal numbers in the naming of our products, i.e., 5, 6, 7, 8, and 12. (See product descriptions on the following pages.) Optical bsorbance (UFS) Optical bsorbance (UFS) Purity is a Key ngredient S-Series 200 nm 210 nm Q-Series 200 nm 210 nm S5 S6 S7 S Q5 Q6 Q7 Q Purity is of key importance in the manufacture of our on Pair Reagents. Regis S- and Q- Series products are synthesized in accordance with the industry s highest quality standards, S Q resulting in exceptional purity and integrity. H3N This is demonstrated in table 1: UV transparency H3OH as low as 200 nm can be achieved for both Table 1. Typical optical absorbances (UFS) at M. the S- and Q-Series reagents. n most cases, these absorbances are lower than those for HPL grade acetonitrile and methanol. lthough the S- and Q-Series ion pair reagents can be used at wavelengths less than 210 nm, the crucial factors in determining what wavelength to use are the integrity of the detector optics and the purity of the organic modifiers. Regis also supplies bulk Sulfonate and several additional bulk on Pair Reagents and Rivier uffers to complement the separation capabilities of the Sulfonate S-Series and Quaternary mine Q-Series. 49

4 ULTRPURE ON PRNG REGENTS ND UFFERS How to Select a Regis on Pair Reagent For Method Development To choose the proper reagent, alkyl chain lengths must be taken into consideration. The chain lengths enable selective separation of the analyte. The longer the chain, the more hydrophobic the counterion, and therefore, greater the retention. Retention may increase by a factor of almost 20 when going from pentyl (Q5) to dodecyl (Q12), as illustrated in table 2 and figure 3. oth table 2 and figure 3 demonstrate that the Q-reagent chain length governs benzoic acid retention times, but does not affect the benzyl alcohol retention times. Similar behavior can also be achieved with the S-Series. The following are guidelines to developing a successful method using Regis ion pair reagents: Select a column endcapped ODS (octadecylsilyl) is most common. Use only HPL-grade water and chromatography grade reagents in mobile phase preparation. hoose the mobile phase components and concentrations that give the best separation. f nonionic components are present in the sample, optimize the resolution prior to attempting ionic separations. Select the appropriate ion pair series to provide the necessary counterion. Use the Q-series for acidic compounds and the S-series for basic compounds. Through a process of elimination, choose the alkyl chain length which results in the best separation (figure 4). Once the reagent has been selected, adjust the ph of the mobile phase to maximize resolution. ecause slight modification of ph can profoundly effect retention and selectivity, make all adjustments in small increments and monitor carefully (table 3). deally, the ion pair reagent concentration in the mobile phase should be M. However, small adjustments in reagent concentration may increase retention slightly and optimize the separation (figure 5). Retention Times (min) Retention Ratio Q-Series enzoic cid enzyl lcohol cid/lcohol Q Q Q Q Q Table 2. Retention vs. chain length. [benzoic acid/benzyl alcohol in (60/40) water/methanol] Q6 Q7 Q8 ph R ph R ph R Table 3. Retention ratio R as a function of ph. Effect of Q-Reagent hain Length on Retention hoosing ppropriate on Pair Reagents,, V No Q Q5 No Q V Q6 Fine-Tuning a Separation Q5 Q7 V Q6 Q8 olumn:, Q12 Mobile Phase: Flow Rate: olumn: Mobile Phase: Flow Rate: Figure 4. n a mixture of ionic and nonionic compounds, first separate the nonionic compounds from each other (See above). Then choose the ion pair reagent that retains the ionic compounds as desired. Here, Q6 seems to be the reagent of choice since all peaks are visibly separated. olumn: Rexchrom ODS 15 cm x 4.6 mm i.d., fully endcapped Mobile Phase: (60/40) water/methanol + Q-Series Flow Rate: 0.6 ml/min ncreasing Q7 concentration from M (left) to M (right) moves the benzoate peak off the benzyl alcohol peak. Figure 5. ncreasing the Q-Reagent concentration may increase retention slightly and optimize the separation., V Q7 Q8 KEY = benzoate = benzyl alcohol Rexchrom ODS 15 cm x 4.6 mm i.d., fully endcapped (60/40) water/methanol M Q-Series 0.6 ml/min Figure 3. Retention increases with Q-Reagent chain length. KEY cids: = isophthalic = phthalic = benzoic V = 1-naphthalene sulfonic lcohols: = benzyl = o-methylbenzyl = p-methylbenzyl Rexchrom ODS 15 cm x 4.6 mm i.d., fully endcapped (60/40) water/methanol M Q-Series 0.6 ml/min.005m.0055m 50

5 REGS SULFONTES (S-SERES) FOR S OMPOUNDS S-Series on Pair oncentrates (For ations) The sulfonates are sodium salts that act as an anionic counterion for the separation and resolution of positively charged analytes. The sulfonates are available as: on pair concentrates premixed 0.5 M solutions of alkyl sulfonates. When diluted to 1 L with HPL-grade water, a 10 ml bottle forms a M solution. Larger quantities are available upon request. Please call Regis for pricing. S5 (1-pentylsodiumsulfonate) (5) 10 ml bottles ml bottle S6 (1-hexylsodiumsulfonate) (5) 10 ml bottles ml bottle S7 (1-heptylsodiumsulfonate) (5) 10 ml bottles ml bottle S8 (1-octylsodiumsulfonate) (5) 10 ml bottles ml bottle S12 (1-dodecylsodiumsulfonate) (5) 10 ml bottles ml bottle M solutions of lkyl Sulfonates (Each 10 ml bottle, diluted to 1 L, produces a M solution) S-Series Method Development Kit Each kit contains a 10 ml bottle of each of the following: S5, S6, S7, S8, S ulk on Pair Reagents (For ations) ulk powder fine, purified crystals, for use as a buffer in large-scale mobile phase preparation. Larger quantities are available upon request. Please call Regis for pricing. 1-Pentanesulfonate, Sodium Salt 25 gm gm Hexanesulfonate, Sodium Salt 25 gm gm Heptanesulfonate, Sodium Salt 25 gm gm Octanesulfonate, Sodium Salt 25 gm gm Dodecanesulfonate, Sodium Salt 5 gm gm ON PR PPLTONS Separation of atecholamines using on Pair Reagents Separation of rtificial Sweeteners olumn: REXHROM ODS, 5µm, 100Å 15 cm x 4.6 mm i.d. Mobile Phase: (89/11) M S8 ion pair concentrate/ acetonitrile, ph 2.5 Flow Rate: 1.0 ml/min Load: 10 µl Detection: UV 280 nm Peak dentities:. 3,4-Dihydroxyphenylacetic acid. Norepinephrine. 3,4-Dihydroxyphenylalanine D. Epinephrine E. 3,4-Dihydroxybenzylamine F. Dopamine D E F olumn: REXHROM Little hamp (ODS), 3µm, 100Å 5 cm x 4.6 mm i.d. Mobile Phase: (86/14) M Q7 ion pair concentrate/ acetonitrile, ph 6.2 Flow Rate: 1.0 ml/min Load: 10 µl Detection: UV 210 nm Peak dentities:. spartame. cesulfame Potassium (cesulfame-k). Saccharin TME (MN) TME (MN) 51

6 REGS QUTERNRY MNES (Q-SERES) FOR D OMPOUNDS Q-Series on Pair oncentrates (For nions) The Q-series is comprised of quaternary alkyltriethylamines that can be used for the resolution of negatively charged species. This unique set of cationic reagents was developed to complement the Sulfonate Series (S-Series) and is exclusively manufactured by Regis. The Quaternary lkyltriethylamines are available as: on pair concentrates premixed 0.5 M solutions of alkyl amines. When diluted to 1 L with HPL-grade water, a 10 ml bottle forms a M buffered solution. Q5 (1-pentyltriethylammonium phosphate) (5) 10 ml bottles ml bottle Q6 (1-hexyltriethylammonium phosphate) (5) 10 ml bottles ml bottle Q7 (1-heptyltriethylammonium phosphate) (5) 10 ml bottles ml bottle Q8 (1-octyltriethylammonium phosphate) (5) 10 ml bottles ml bottle Q12 (1-dodecyltriethylammonium phosphate) (5) 10 ml bottles ml bottle M solutions of Quaternary lkyltriethylamines (Each 10 ml bottle, diluted to 1 L, produces a M solution) Q-Series Method Development Kit Each kit contains a 10 ml bottle of each of the following: Q5, Q6, Q7, Q8, Q Other Regis ulk on Pair Reagents (For nions) Other bulk on Pair reagents such as Tetrabutylammonium phosphate, Trihexylamine and Triheptylamine are complementary reagents used for the resolution of negatively charged analytes. Tetrabutylammonium phosphate 0.5 M, ph ml Tetrabutylammonium phosphate 0.5 M, ph ml on Pair References 1. Perry, J..; Glunz, L. G.; Szczerba, T. J.; Hocson, V. S.; Reagents For on Pair Reversed-Phase HPL; merican Laboratory 1984, 16(10), Eksborg, S.; Lagerstrom, P.; Modin, R.; Schill, G.; on Pair hromatography of Organic ompounds J. hrom. 1973, 83, Eksborg, S.; Schill, G.; on Pair Partition hromatography of Organic mmonium ompounds nal. hem. 1973, 45, For additional information on on Pair Reagents, check our Web site at or contact Regis directly at: (800) ext. 649 (847) ext us at: sales@registech.com. 52